Such a cool truck!!! At this stage of the game most all the finishing touches boil down to personal preference...it's your truck, so your preference! LOL!

Based on the 2 pics you posted, the tire size looks pretty good to me. Like Whiplash said, they fill the wheel well up nicely. If you go shorter on the rear, you'll probably need shorter on the front, too because more gap between the tire and fender on the rear will make the front tires look too tall with no gap. Perhaps the tire shop would mount up a couple different sizes and let you look at it before you decide.

The front bumper is innovative but also a tough call since the truck looks so cool without one... Sure it might offer a little protection if you bump into a pole at low speed but otherwise, not much. I'd probably keep it the matte silver or give it some kind of patina that doesn't draw attention to it and looks like it's been on there a while. The front fenders & grille are too great and don't need the distraction

Of course, these are just my opinions and you know what they say about opinions....Hahaha!!

Awesome truck! Great work!!